Siloxane polymers are known to be fully resistant to dry etching and plasma. The use of siloxane polymers as resist material has been reported in the literature.
One example is a composition comprising an organosiloxane having many silanol groups and a compound capable of generating an acid in response to light. While the silanol groups serve as an alkali-soluble group, the acid generated upon light exposure acts as a silanol condensation catalyst. Thus light-irradiated areas undergo condensation cure, forming a negative pattern. See Proc. SPIE 1672, 56 (1992).
Also known is a positive resist material based on an organopolysiloxane of siloxane bond backbone wherein organic groups bonded to silicon have hydroxyl groups, some hydrogen atoms of which are substituted by acid labile groups. Exemplary are a resist resin composition comprising a polyorganosilsesquioxane having acid-labile ester groups on side chains (JP-A 11-60733) and a resist composition comprising poly(2-hydroxycarbonylethyl)siloxane in which some hydroxyl groups are protected with acid labile groups (JP 3175514). These resist compositions using conventional siloxane polymers do not fully meet the properties required of resist materials including resolution, sensitivity and development performance.
Interlayer dielectric films and pattern-forming materials currently used with TFTs in LCDs are required to have high heat resistance, high transparency, low dielectric constant and solvent resistance. Prior art materials known to meet such properties include a positive heat-curable photosensitive composition comprising an alkali-soluble phenolic resin, a quinonediazide compound, a heat curing agent, and an acetate solvent having a boiling point of up to 150° C. (JP-A 7-98502) and a positive photosensitive resin composition comprising an alkali-soluble phenolic resin, a quinonediazide compound, a crosslinking agent, and a thermoacid generator (JP-A 2004-240144). However, these materials may have poor heat resistance and transparency and sometimes lack chemical resistance.
On the other hand, a certain material is designed to take advantage of the heat resistance, low dielectric constant and similar characteristics siloxane polymers possess. Examples include a photosensitive composition comprising a polysiloxane compound containing siloxane units derived from a cyclization addition reaction product and a quinonediazide compound (JP 2648969), a positive resist composition comprising an alkali-soluble siloxane polymer having phenolic hydroxyl groups and a quinonediazide compound (JP-A 2003-255546), and a photosensitive resin composition comprising a siloxane polymer, a quinonediazide compound, finely divided silica, and a solvent (JP-A 2007-41361). However, these compositions, when heat cured, can be colored with decomposition products of the quinonediazide compound, resulting in cured films becoming less transparent.